The present invention relates to an improved device and method for welding plastic battery jar covers onto plastic battery jars. Specifically, this invention relates to means for pressing the molten bead, created between the battery jar and the battery cover during welding, flat against the cover and the jar interface until said molten bead solidifies.
In U.S. Pat. No. 4,352,977 entitled "Welding Apparatus and Method", an apparatus and method for welding battery covers onto battery jars are disclosed. Said Patent, the disclosures of which are incorporated herein by reference, discloses and claims an apparatus which comprises a main frame, a work zone having loading, welding and unloading stations, means for moving containers to be welded successively from said loading station to said welding station and from said welding station to said unloading station, welding means for positioning and controlling the relationship between the cover and the jar during welding and for forming a welded joint wherein said welding means includes a heating assembly and a clamping assembly, drive means for operating the apparatus and contact means for activating the drive means in a predetermined sequence.
While the apparatus and method disclosed in U.S. Pat. No. 4,352,977 performs satisfactorily, it has been found that when a thermoplastic hot-plate weld is accomplished using said apparatus and method, the melting process causes molten material to form a bead on each side of the interface between the cover and the jar. Under present practices, the outer bead must be cut off or trimmed after the weld has been made and the plastic solidified so that the battery cell will fit into a steel container or tray with other battery cells. It is believed that the cutting or trimming process can open up small weld line imperfections which can result in microscopic leak paths which permit electrolytes (sulfuric acid) to escape the cell causing corrosion problems as well as contributing to the short-circuiting of the battery.